Remote procedure call

Please note that layers and tiers are two different concepts. Tiers mean the physical separation of subsystems—each subsystem runs on a different hardware or the same hardware but in different processes. In a multitiered system, the interaction between the subsystems is accomplished through remote procedure calls (RPCs). Any RPC involves network overhead and therefore has a performance penalty whether the remote procedure is on a separate hardware or on the same physical hardware but in a different process. Layers, on the other hand, are logical separations of the subsystems. Each layer can run on a different physical tier, or all layers can run on a single tier. The purpose of physical tiers is to leverage distributed hardware resources or to reuse a piece of software that is deployed on a different hardware that your system wants to leverage. The purpose of layered software architecture is to separate the system into highly cohesive and loosely coupled modules (see Chapter 2 for software development principles). 

The communication method facilitating interactions between a client and a server is the most important part of a C/S system. For easy development of the C/S systems, it is important for processes located on physically distributed computers to be seen as if they were placed in the same machine. Socket, remote procedure call, and CORBA are the main interfaces that realize such transparent communications between distributed processes. 

SOAP A protocol for exchanging structured and typed information between networked computers, especially in web services over the Internet. SOAP messages are formatted in XML and generally use HTTP as their transport protocol the most common type is the remote procedure call. 

Birrell AD, Nelson BJ (1983) Implementing remote procedure calls. XEROX CSL-83-7... 

A few remote procedure call (RPC)-based service.s. such as NIS (network information service) or NFS (network file system, both explained below) use UDP. TCP is a bl-directlonal, stream-oriented protocol, A constantly open communication channel is maintained between two programs communicating via TCP. Standard data appears at the receiver s side with some delay in exactly the same sequence as produced by the sender. Very small urgent messages (out-of-band-data) can be transmitted outside of the normal sequential order. 

Here there is a difference between DCOM and CORBA, Microsoft uses MIDL, while CORBA uses CORBA IDL. Objects talk to each other across the network, using ORB (for CORBA) and Microsoft uses different DCOM products. Multiple CORBA ORBs communicate via a standard communications protocol known as Internet Inter-ORB Protocol (HOP) as shown in figure A2-4, while Microsoft uses DCOM protocol as shown in figure A2-5. EJB uses its own standard communication for Java-to-Java communication called Remote Method Invocation (RMI). The term BOA is used for Basic Object Adapter and RPC is used for Remote Procedure Call . 

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